Electrostatically charging method

ABSTRACT

An electrostatically charging method for charging a light sensitive layer copy sheet, which is positioned close to a charging grid including the steps of generating spike-shaped voltage pulses each having sharp rise and fall portions and a pinpointed peak, and applying said pulses to the charging grid for generating a corona thereat, and thereby imparting an electrostatic charge to the light sensitive layer of the copy sheet.

United States Patent Inventor Masanari Suzuki Kanagawa-ken, Japan Appl.No. 821,699

Filed May 5, 1969 Patented Oct. 12, 1971 Assignee Kabushiki Kaisha RicohTokyo, Japan Priority May 8, 1968 Japan 43/30703 ELECTROSTATICALLYCHARGING METHOD 5 Claims, 4 Drawing Figs.

US. Cl ..250/49.5 ZC

Int. Cl G03g 13/02, 603g 15/02 Field of Search 250/495 C; 317/262 ACORONA" GENORATING VOLTAGE UNITED STATES PATENTS 3,076,092 l/1963 Mott250/49.5 3,390,266 6/1968 Epping 250/495 Primary Examiner-William F.Lindquist Attorney-Burgess, Ryan and Hicks ABSTRACT: Anelectrostatically charging method for charging a light sensitive layercopy sheet, which is positioned close to a charging grid including thesteps of generating spikeshaped voltage pulses each having sharp riseand fall portions and a pinpointed peak, and applying said pulses to thecharging grid for generating a corona thereat, and thereby imparting anelectrostatic charge to the light sensitive layer of the copy sheet.

PATENTEUnm 12 l97| I 3.612.862

CORONA" GENORATING VOLTAGE FIG.2A

CORONA E V POSITIVE CORONA 1) NEGATIVE CORONA AND 3.

FIG. 20

- NEGATIvE G) 'INVENTOR MASANARI Suzum ELECTROSTATICALLY CHARGING METHODBACKGROUND OF THE INVENTION The present invention relates to anelectrostatically charging method and more particularly to a method foruse in electronic photography for imparting the electrostatic charge bythe corona discharge to a light-sensitized layer of a copy sheet.

In the electrostatic charge imparting-type electronic photography, it isgenerally required that the light-sensitized layer of a copy sheet isimparted with the electrostatic charge immediately prior to itsexposure. In the conventional method of the type described above, a pairof wire or needle electrodes are disposed so as to be spaced apart froma copy sheet interposed therebetween by a suitable distance and avoltage ranging from 5 to 7 kv. is applied across the pair of electrodesso as to generate the corona discharge, thereby electrostaticallycharging the sensitized layer by the ions generated by the coronadischarge. In this case, the positive electrode generates the positivecorona, that is, the positive ions, while the negative electrode, thenegative corona, that is, the negative ions. Depending upon the typesand properties of the sensitized layer of copy sheets, either of thepositive or negative corona discharges is utilized. For example, whenthe sensitized layer is mainly composed of ZnO, the negative dischargeis utilized while in case of the sensitized layer consisting of Se, thepositive corona discharge is utilized. In case of an electricallyconductive copy sheet having a layer of ZnO upon its one surface, thecopy sheet is first placed upon an electrically conductive substrate orsupport with the sensitized layer being directed upwardly and a wireelectrode is vertically upwardly spaced apart from the sensitized layerby 10 to mm. so that the sensitized layer may be imparted with theelectrostatic charge by the negative corona discharge generated by thewire electrode. Alternatively, the conductive substrate or support maybe eliminated. That is, the wire electrode is vertically downwardlyspaced apart from the rear surface, that is, the surface opposite to thesensitized layer of the copy sheet by a distance from 10 to 20 mm. sothat the positive corona discharge may be generated, thereby impartingthe electrostatic charge to the copy sheet. In both of the methodsdescribed above, a DC high voltage is applied across a pair ofelectrodes. The invention however had made an extensive study on thewave forms of the voltage applied 'to the electrodes and found out thatthe complete DC is not required for imparting the electrostatic chargeto the sensitized layer and the pulsating voltage is also satisfactorilyused for this purpose. The finding of the inventor has been confirmed bythe experiments.

In case of the sensitized layer consisting of ZnO, the layer is impartedwith the electrostatic charge by the negative corona discharge asdescribed hereinabove. In this case, even if the wire electrode is used,the point corona discharges are generated along the wire electrode sothat the sensitized layer is not uniformly charged. To eliminate thisdefect, the wire electrode must be spaced apart from the sensitizedlayer by a greater distance or a plurality of wire electrodes must beused, resulting in the increased power consumption. This phenomenonoccurs even with DC or pulsating voltage from 50 to I00 c.p.s.

SUMMARY OF THE INVENTION In brief, the present invention provides anelectrostatically charging method for use in electronic photographycomprising the step of imparting the electrostatic charge to alight-sensitized layer of a copy sheet by the corona discharge generatedby the periodic or nonperiodic repetitive pulse voltages each having awaveform with sharp rise and fall and a pinpointed peak. This waveformis sometimes called a spike waveform. Any convenient or conventionalpulse generator may be used when carrying out this invention. One suchspike wave-shaped generator is shown in my copending U.S. Pat.application Ser. No. 821,701 which is assigned to the same assignee asthis application.

The advantages accrued of the present invention may be enumerated asfollows:

1. Uniform charging may be ensured and the power consumption can be madeless.

2. Because of the sharp voltage waveform, the initiation of the coronadischarge may be accelerated and the repetitive cycle can be shortenedso that the high-speed charging may be effected.

3. The pulse voltage is sufficiently high enough for generating thecorona discharge, but the energy is less so that the electric shock canbe minimized. Even if the spark discharge should be initiated, thesensitized layer will be less damaged.

4. Both of the high-frequency harmonics and the repetitive frequency ofthe pulse voltage are high so that the coils and other components may bemade compact in size.

5. In order to control the magnitude of charge, that is the potential ofthe sensitized layer, the voltage is increased or the electrode gap isadjusted in case of a sinusoidal wavefonn voltage such as commerciallyavailable voltage. In this case, the voltage tends to rise up to a sparkdischarge potential resulting in the breakdowns of the sensitizedlayers. However, according to the present invention, the above controlmay be made only by adjusting the repetitive frequency of the pulsevoltage. This simple adjustment method also serves to make the devicesimple in construction and compact in size.

BRIEF DESCRIPTION OF DRAWING FIG. I shows various waveforms used incorona discharge for explanation and comparison with the charging methodof the present invention, and

FIG. 2 shows schematically corona discharges by wire electrodes appliedwith the voltages having the waveforms as shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 showingvarious waveforms used in corona discharge for comparison, the voltagesare plotted against the time, plotting on the abscissa the time and onthe ordinate the voltage. The voltage waveform used in the presentinyention is of pulse having sharp rise and fall as shown bymThewaveform@is of the voltage obtained from a commercial power source or asinusoidal waveform generator while the waveformQDis generated by arelaxation oscillator. The half sinusoid waveform 2 is typically 60cycles per second. It will be noted that the corona-generating voltage Iis much faster than the waveform 2.

FIGS. 2-A, B and C are for illustration of the states of the coronadischarge generation by wire electrodes E. In case of the positivecorona discharge, as shown in FIG. Z-A, the corona discharge generallysurrounds the wire-shaped electrode E regardless of the waveforms of thevoltages applied thereto. However, in case of the negative coronadischarge, as shown in FIG. 2-B, the point-corona discharges areobserved along the wire electrode E so that the light-sensitized layeris not uniformly imparted with the electrostatic charge as describedhereinbefore. In order to avoid such nonuniform charging, the wireelectrode must be spaced apart from the sensitized layer by agreaterdistance or a plurality of wire electrodes must be disposed,resulting in the increase of the required power. The above undesirablephenomenon is observed especially when the frequency of the voltageapplied to the wire electrode pulsates at a rate from 50 to I00 c.p.s.even if the waveforms@and@are varied as shown in FIG. 1.

According to the charging method utilizing the pulse voltageQas shown inFIG. I of the present invention, the pointcorona discharges similar tothose shown in FIG. Z-B are generated in case of the negative coronadischarge, but the number of such discharges is remarkably increased ascompared with that shown in FIG. Z-B. That is, one corona discharge isgenerated per length of l to 2 cm. in FIG. Z-B while in FIG. 2-C showingthe method of the present invention 3 to 4 corona discharges aregenerated per length of 1 to 2 cm.

Furthermore, according to the present invention, the positive coronadischarge surrounding the electrode as shown in FIG. 2-A may besubstantially approximated even in case of the negative corona dischargeby increasing the repetitive rate of the pulse voltage, so that theuniform charging may be ensured and the electrode may be closelypositioned toward the sensitized layer, thereby reducing the requiredpower.

The present invention has been so far described with particularreference to the preferred embodiment thereof, but it is to beunderstood that the variations and modifications can be effected withoutdeparting the true spirit of the present invention as describedhereinabove and as defined in the appended claims.

lclaim:

1. An electrostatic charging method for imparting electrostatic chargeto a light-sensitive layer copy sheet which is positioned close to acharging grid, comprising the steps of generating voltage pulses, eachpulse having a spike shape with sharp rise and fall portions, andpinpointed peaks;

applying said voltage to the charging grid for generating a coronadischarge by said voltage pulses on said grid and thereby impartingelectrostatic charge to a light-sensitive layer copy sheet. 2. A methodaccording to claim 1, including the step of generating said pulsesperiodically.

3. A method according to claim 2, including the step of varying thefrequency of said pulses to control the corona.

4. A method according to claim 1, including the step of generating saidpulses repetitively and nonperiodically.

5. A method according to claim 4, including the step of varying therepetition rate of said pulses to control the corona.

2. A method according to claim 1, including the step of generating saidpulses periodically.
 3. A method according to claim 2, including thestep of varying the frequency of said pulses to control the corona.
 4. Amethod according to claim 1, including the step of generating saidpulses repetitively and nonperiodically.
 5. A method according to claim4, including the step of varying the repetition rate of said pulses tocontrol the corona.